Amendment 2 and AFDD's

[IAmSparkytus!]

I don't see current prices being sustained for long, should manufactured quantities significantly increase, and expect most to be on the market at the sort of prices RCBOs were a couple of years ago - although that's an entirely separate issue from the actual effectiveness of AFDDs.

The £2000 I came up with was based on a domestic install as well and I don't even do any domestic work!

We usually install anything from 36-way to 72-way boards. Imagine the cost to populate one of those ?‍?

 

[suffolkspark]

The stupid thing is it's the 40-50A shower circuits that sit arcing their selves to death on loose shower pull cords that I find.. but circuits that size don't have to be done

 

[nicebutdim]

The £2000 I came up with was based on a domestic install as well and I don't even do any domestic work!

We usually install anything from 36-way to 72-way boards. Imagine the cost to populate one of those ?‍?

Presently I see prices upwards of £100 for a single RCBO/AFDD, but would guess £30 per unit might be likely in a few years - obviously dependant on widespread uptake.

 

[IAmSparkytus!]

RCBOs alone are £30ish at the minute so wouldn't they be slightly more expensive with the added AFD tech?

 

[nicebutdim]

I'm using rough prices as an example as RCBOs are available from just over £10 per unit to quite expensive. The point was that prices will drop considerably from current levels, once manufacturing is ramped up.

Having watched John Ward and David Savery prove their general lack of effectiveness, I remain unconvinced of their usefulness in domestic DBs.

 

[Cookie]

But are they?

I have seen comments by some of the USA folk like @Megawatt and @Cookie to the effect they are unreliable and a significant source of problem trips, even to the point of being fitted for new installation inspection and then changed back to GFCI (RCD) afterwards.

Key here is the cost/benefit question. We can see the current costs and, while that will probably drop, it is going to be a big factor for some time on the affordability of professional electrical work. But what of the benefits? Has anyone got a proper analysis of how many fires they might stop to justify the cost?

Critically many "electrical fires" are appliances like tumble dryers with lint catching fire, or motor run caps (and similar) going up in flames, and AFDD would do nothing there.

The argument "If it saves one life" is misleading because by mandating AFDD a significant number of poor / dodgy installations simply won't be updated as they become unaffordable and so there is a real risk of a greater number of accidents due to a lack of RCD or other cheaper improvements that could have been done in-budget. I find it rather strange there is not any proper analysis being put forward to justify them even by the manufacturers, but maybe I just have not seen it.

You would be correct, AFCI in the US are a constant never ending battle of nuisance tripping. To make matter worse we find burned up splices, screws, terminals and sockets where the combination AFCI breaker (serial+parallel arcing protection) never tripped.

With that said I want to simply state two facts:

1) earth fault loop impedance and RCDs provide the exact same level of parallel arcing protection as AFDDs.

2) Serial arcing is the end stage of joule heating, assuming fire hasn't already ensued.

 

[Sisyphus]

You would be correct, AFCI in the US are a constant never ending battle of nuisance tripping. To make matter worse we find burned up splices, screws, terminals and sockets where the combination AFCI breaker (serial+parallel arcing protection) never tripped.

With that said I want to simply state two facts:

1) earth fault loop impedance and RCDs provide the exact same level of parallel arcing protection as AFDDs.

2) Serial arcing is the end stage of joule heating, assuming fire hasn't already ensued.

Maybe a dumb Q , but i'm not quite sure what the 'RCD" vs 'AFCI difference is Cookie....

~S~

 

[pc1966]

Maybe a dumb Q , but i'm not quite sure what the 'RCD" vs 'AFCI difference is Cookie....

~S~

In the UK we refer to an RCD (residual current device), where as in the USA it is GFCI (ground fault circuit interrupter). If you have a partial fault to earth/ground then it will disconnect quickly and so stop a modest fault getting hot enough to start a fire.

With a hard high-current fault then the OCPD (over current protection device, i.e. fuse or circuit breaker) should also disconnect fast. In the UK that aspect of design is deeply embedded in the wiring regulations and the way that any professional electrical will test a circuit before and after putting it in to use (energising it). Before we would check the DC resistance of the line and earth cables (known as R1 and R2) and check that the supply impedance Ze along with R1+R2 is low enough to force disconnection in under 0.4s (typically, can be more or less in specific cases) under worst case of low supply volts and cables at max working temperature. After we would measure the supply impedance at the end point Zs (which should be Ze + R1 + R2)

We in the UK are now seeing AFDD = AFCI being introduced and they are intended to detect the high frequency 'buzz' of an arcing fault, with the aim of stopping it before it becomes a fire. Problem is a lot of things arc normally, like switch, relays, or some muppet plugging in or removing live. So they have to balance sensitivity and detection approach to try and trip on real fault arcs, but not on normal operating arc. Tricky...

Another difference between the UK and the USA (I think, not qualified in the ways of US electrical code) is the norm in UK/EU is to put the RCD or AFDD in the distribution board, where as I believe the USA favours them at outlet sockets. That seems odd and a poor choice to me, as more expensive and no protection for faults on the fixed wiring. Maybe some USA members like @Cookie or @Megawatt can comment on this aspect in case I'm hopelessly wrong.

 

[Cookie]

Maybe a dumb Q , but i'm not quite sure what the 'RCD" vs 'AFCI difference is Cookie....

~S~

Any arcing to earth produces a current imbalance which trips the RCD. You don't need to look at the current signature on the active to do that, nor does said current signature analysis need to discriminate between a vacuum cleaner motor vs an actual fault.

 

[Sisyphus]

In the UK we refer to an RCD (residual current device), where as in the USA it is GFCI (ground fault circuit interrupter). If you have a partial fault to earth/ground then it will disconnect quickly and so stop a modest fault getting hot enough to start a fire.

With a hard high-current fault then the OCPD (over current protection device, i.e. fuse or circuit breaker) should also disconnect fast. In the UK that aspect of design is deeply embedded in the wiring regulations and the way that any professional electrical will test a circuit before and after putting it in to use (energising it). Before we would check the DC resistance of the line and earth cables (known as R1 and R2) and check that the supply impedance Ze along with R1+R2 is low enough to force disconnection in under 0.4s (typically, can be more or less in specific cases) under worst case of low supply volts and cables at max working temperature. After we would measure the supply impedance at the end point Zs (which should be Ze + R1 + R2)

We in the UK are now seeing AFDD = AFCI being introduced and they are intended to detect the high frequency 'buzz' of an arcing fault, with the aim of stopping it before it becomes a fire. Problem is a lot of things arc normally, like switch, relays, or some muppet plugging in or removing live. So they have to balance sensitivity and detection approach to try and trip on real fault arcs, but not on normal operating arc. Tricky...

Another difference between the UK and the USA (I think, not qualified in the ways of US electrical code) is the norm in UK/EU is to put the RCD or AFDD in the distribution board, where as I believe the USA favours them at outlet sockets. That seems odd and a poor choice to me, as more expensive and no protection for faults on the fixed wiring. Maybe some USA members like @Cookie or @Megawatt can comment on this aspect in case I'm hopelessly wrong.

well this is interesting, and thx for your reply pc1966...

fwiw, i'm a US spark, don't really know much other than what i'm shown here

Yet i'm reading that you folks over the 'pond' seem far more aware of any given circuit's ~R~ factor

As well as mag trip times..........so this would seem the crux , or specific science behind either 'enhanced' OCPD , be it on your turf or mine... ~S~

 

[IAmSparkytus!]

When are they looking at bringing amendment 2 into play and will the changes be announced prior to that?

 

[newfutile]

it comes out on 28th March 2022 there is usually a 6 month overlap after that

 

[Sisyphus]

Any arcing to earth produces a current imbalance which trips the RCD. You don't need to look at the current signature on the active to do that, nor does said current signature analysis need to discriminate between a vacuum cleaner motor vs an actual fault.

isn't that the sdame for an afci?

~S~

 

[pc1966]

isn't that the sdame for an afci?

Not quite.

An RCD will detect a "parallel arc" between L & E, as well as simple leakage due to non-arcing conduction. But it won't detect a fault between L & N (that is below the OCPD) nor a series arc where a small break in L or N has happened.

An AFDD should pick up the high frequency content of the arc and so trip on L-N faults and series arc faults. But other things also produce arc noise.

 

[Aaron b]

If they don't work on ring circuits and not required over 32amp and ineffective on lighting circuits afdds seem pointless.

 

[Sisyphus]

Not quite.

An RCD will detect a "parallel arc" between L & E, as well as simple leakage due to non-arcing conduction. But it won't detect a fault between L & N (that is below the OCPD) nor a series arc where a small break in L or N has happened.

An AFDD should pick up the high frequency content of the arc and so trip on L-N faults and series arc faults. But other things also produce arc noise.

thx PC
i had thought the main component was the same, a toroid .......at least to the extent of my reading......

as ro the 'frequency' and/or arc waveform, we're told our AFCI incorporates a microprocessor with special algorithm software

the details of which, we're not privy to, but the testing lab methods we are>>>

This is what they used....a 'simulator;'.....

https://i.Upload the image directly to the thread.com/eOF06wB.jpg
Do RCD's have this manner of testing?

~S~

 

[pc1966]

The AFDD probably have a toroid as well, but it would need to be another in (probably) the L so it can detect the faults that a RCD is designed not to (L-N flow). By frequency I mean a typical earth faults sees a lot of 50Hz flow, but an arc typically has components to over 10kHz.

As far testing - that is a sore point. In the UK electricians typically have a Multi Function Tester (so high voltage IR, few 100mA bond resistance, supply Zs, RCD trip, voltage, and probably phase rotation, maybe earth rod impedance via two spikes, etc) but I have not seen much sign of them being available to test AFDD. We are being told to trust the self-test button, etc. Yes, what a good idea...

 

[pc1966]

If they don't work on ring circuits and not required over 32amp and ineffective on lighting circuits afdds seem pointless.

I can see some cases for them, but the cost/benefit looks very poor to me.

They do work on RFC but don't detect an open ring as practically no arcing takes place there as voltage difference is very small, however, they should detect arc faults on appliance cables that are attached that are above the few amps threshold.

But again, where is the evidence for their use? That is a proper analysis of fire (or near fire fault) cases that clearly would have been stopped by an AFDD and not things like lint fires in tumble dryers, etc.

 

[pc1966]

Broken web site duplicate post
stupid 50 character limit

 

[IAmSparkytus!]

Is anyone else having problems with the website? This is the only place it's letting me click on/post a message! ?